In an array-fed reflector antenna device that is a combination of a reflecting antenna and an array antenna, it is necessary to set an appropriate excitation amplitude and an appropriate phase for each of element antennas which construct the array antenna in order to provide a beam in a desired direction. Conventionally, an excitation phase or excitation amplitude phase for all the element antennas is determined numerically so as to form a beam in a desired direction. Further, a method of determining an excitation amplitude phase efficiently by limiting the range of element antennas to be excited is also disclosed (for example, refer to patent reference 1).